This invention relates generally to heating, ventilation and air conditioning (HVAC) systems and, more particularly, to such systems as they relate to automotive passenger compartment climate control. More specifically, this invention deals with the accurate sensing of automotive passenger compartment ambient temperature and heat energy levels wherein such sensing is necessary to establish and maintain comfort level within the passenger compartment.
It is common practice in automotive climate control to utilize passenger compartment air drawn across a temperature sensor through an aspirator hose concealed behind the instrument panel to obtain a convective measure of passenger compartment thermal level. Such systems are typically assembly intensive, subject to hardware failures such as aspirator hose disconnects and material obstruction preventing air flow. Such failures, all of which alter the air flow across the temperature sensor, tend to result in performance degradation and inaccuracy but do not result in catastrophic system failures. Consequently, passengers will feel dissatisfied with the performance of the HVAC system yet not realize that it is operating at reduced performance quality.
An automobile's instrument panel typically houses a temperature sensor over which air from the vicinity of the instrument panel is drawn. Additionally, an automobile instrument panel is a carrier for many heat generating components, such as radios, instrumentation, various electronic modules and back lighting. All of these, especially when evening driving is encountered, may result in a thermal load local to the instrument panel that is not indicative of the thermal level of the passenger compartment which is the desired temperature to be measured. This may result in false readings at the temperature sensor. However, an instrument panel remains a desirable location for sensing media.
Frequently, HVAC control systems additionally rely upon a second sensor to detect a solar load for use as a corrective control signal. Outside air temperature is often likewise utilized as another corrective control signal. These of course add complexity to the HVAC control system and in the case of a sun load sensor may be cosmetically unappealing since one is typically mounted on an upper surface of an instrument panel or is exposed therethrough.